configs/mangopi_mq1rdw1_defconfig: fix build failure due to undefined linux headers

Add BR2_PACKAGE_HOST_LINUX_HEADERS_CUSTOM_6_6 to prevent error:
Incorrect selection of kernel headers: expected 6.8.x, got 6.6.x

Fixes:
https://gitlab.com/buildroot.org/buildroot/-/jobs/6498278078

Signed-off-by: Giulio Benetti <giulio.benetti@benettiengineering.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
1 file changed